Honestly, I love the idea. Of course, this gadget isn’t supposed to replace a real computer. As @Akito pointed out, the keyboard is probably not so great for typing. However, let’s be honest, most notebooks have crappy keyboards and at least some people seem to like the Pi keyboards, as e.g. Chris from Explaining Computers points out in his always very charming way.
I could imagine that this is very nice to connect to a TV (e.g. for children) and perhaps to some external devices in the living room and it might also be a nice thing to carry to off-site meetings: much lighter than a laptop and more user-friendly than a phone.